This invention relates to traveling wave tubes and more particularly to the slow wave structure of a traveling wave tube which is required in order to couple the incoming microwave energy at several tens of gigahertz frequency to the electron beam of the traveling wave tube in order to thereby amplify the incoming microwave energy and to remove the amplified microwave energy at the other end of the slow wave structure.
The desirability of a helical waveguide for providing a slow wave structure has been recognized for many years. The structure of the helical waveguide of this invention consists of half of a rectangular center ridge waveguide wound around in a spiral with a hole down the center for an electron beam. The fundamental mode of propagation of the waveguide is effectively slowed relative to the axial movement of electrons by causing the propagating RF energy to follow the spiral pathway.
Although conceptually simple in design, the problem is how to make such a helical waveguide structure, especially for high frequency tubes where the waveguide dimensions are measured from hundredths of inches.